A world types mod for Minecraft Beta 1.7.3. I am publishing this as I'm not likely of finishing this up. Expect all sorts of bugs and lack of multiplayer version.
Set up a MCP 4.3 (or anything that uses MCP mappings) environment with ModLoader, ShockAhPI 5.1 and OverrideAPI 1.0.1
Copy contents of the src folder to the root of your MCP environment and you're done!